Imaging system for vehicle headlamp control

ABSTRACT

An imaging system for use in a vehicle headlamp control system includes an opening, an image sensor, a red lens blocking red complement light between the opening and the image sensor, and a red complement lens blocking red light between the opening and the image sensor. Each lens focuses light onto a different subwindow of the image sensor. The imaging system allows processing and control logic to detect the presence of headlamps on oncoming vehicles and tail lights on vehicles approached from the rear for the purpose of controlling headlamps. A light sampling lens may be used to redirect light rays from an arc spanning above the vehicle to in front of the vehicle into substantially horizontal rays. The light sampling lens is imaged by the image sensor to produce an indication of light intensity at various elevations. The processing and control logic uses the light intensity to determine whether headlamps should be turned on or off. A shutter may be used to protect elements of the imaging system from excessive light exposure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.09/093,993, entitled “IMAGING SYSTEM FOR VEHICLE HEADLAMP CONTROL,”filed on Jun. 9, 1998, now U.S. Pat. No. 6,130,421, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to imaging systems for use in a controlsystem such as a vehicle headlamp control.

Headlamps illuminate a region in front of a vehicle allowing a driver toview the region when ambient light is insufficient. Headlamps also allowthe vehicle to be seen by pedestrians and drivers of other vehicles.High beam headlamps provide even greater illumination and have a greatercoverage region. However, high beam headlamps may blind drivers inoncoming vehicles and drivers in vehicles traveling in the samedirection within the high beam coverage region. Traditionally, a driverhas had to manually control turning headlamps on and off and switchingbetween high beam and low beam.

One difficulty with manual control is that the driver may forget to turnheadlamps on at dusk making the vehicle difficult to see. Anotherdifficulty is that the driver may neglect to dim high beam headlamps foroncoming traffic or when approaching another vehicle from behind.

Previous attempts to automatically control the operation of vehicleheadlamps have used sensors which provide a single output signal or avery small number of output signals to the associated control system.For example, a single output sensor has been used to sense ambient lightfor determining when to turn headlamps on or off. Also, a single outputsensor has been used for determining when to dim automotive headlampsWhereas headlamp on/off control using a single sensor input has achievedlimited success in automotive applications, a single sensor headlampdimmer control is not currently offered because of its manyshortcomings.

Array imaging sensors and various scanning techniques have beenproposed, but even with the reduced costs made possible by today'selectronics, these sensors and techniques have not produced satisfactoryheadlamp dimming and on/off control functions. Such sensing systemstypically have hundreds of rows and columns of pixel sensors generatinghundreds of thousands or even millions of pixels. At a typical videorate of 30 frames per second, this requires conversion and dataprocessing rates in the millions of operations per second.

Headlamp on/off control can be based on ambient light levels. Headlampdimmer control can be based on recognizing the headlamps from oncomingvehicles and the tail lamps of vehicles approached from behind. Sincethe resolution required to detect ambient light levels and to detectheadlamps and tail lights is less than required for traditional images,a smaller imaging array, and hence, slower processing electronics, maybe used.

In order to distinguish red tail lamps from other lights, the imagingsystem must produce readings in at least two different color bands. Thefirst of two methods usually used to sense colors with an image sensorhas been to cover one-third of the pixel sensing sights in the imagerwith a red or red complement filter, one-third of the pixels with a blueor blue complement filter, and one-third of the pixels with a green orgreen complement filter. This is often done, for example, by placingalternating red, green, and blue stripes over columns of pixels. Eachpixel site registers one color and interpolation is used to supply thetwo missing colors at each pixel sight.

When coupled with a low resolution imager, this technique for sensingcolor creates a problem. Due to the optics used, the projected image ofa headlamp or tail light viewed by the imaging sensing array is verysmall, probably smaller than the resolving power of the lens. Thisprojected image will be referred to as a dot. When pixel spacing issignificantly smaller than the dot size projected by the lens, a portionof a dot of a particular color may not always strike a sensor sight ofthat color. As the pixel size or area of optical coverage per pixel isincreased due to a corresponding reduction in the number of pixels, thevoids between the like colored pixel sights become larger unless acomplicated interdigitated pixel pattern is used. Even if readout of aparticular color is not completely lost by having the entire dot imageprojected on a pixel of another color or colors, the readout will becoarse depending on what portion of the dot strikes a pixel. Sincedistinguishing a color is usually a matter of determining balancebetween two or more color components and not just determining thepresence or absence of a particular color component, when the small spotof light in the projected image of a headlamp or tail light falls moreon one pixel of one color than another, the measured balance is alteredaccordingly.

A further disadvantage with this method results from dyes used toimplement the color filters. The dyes are normally organic and aresubject to degradation from thermal and light exposure. Since the dyesits directly over individual pixel sites, the energy from a stronglight source such as the sun is focused by the lens system directly ontothe dye.

A still further problem with this method is that having the color filterdye applied to and precisely registered with the pixel sensor sight onthe image sensor is expensive. The cost of adding color filters directlyon the pixel sensor may be as expensive as the silicon image sensingchip itself.

A second method for imaging color splits light from the image into red,green, and blue components which are projected onto separate imagesensors, each of which measures its respective color filtered image.This requires a complicated optical arrangement and three separate imagesensors. The color separation technique often utilizes mirrors whichselectively reflect one color and transmit the complementary color.These optical arrangements normally require widely separated non-planarimage sensor sights making it difficult, if not impractical, to placethe three sensors on a common silicon substrate or even in a commonpackage. This technique presents a three-fold problem. A single sensorarray cannot be used, a single silicon chip cannot be used, and a singlepackage cannot be used.

What is needed is a cost effective imaging system to be used in, forexample, a headlamp control system. To limit costs and complexity in theoptics, the sensor array, the processor, and processor interface, aminimal number of pixels, preferably in a range which would beconsidered too small for satisfactory pictorial image presentationshould be used. The imaging system should not use spectral filteringthat would place dyes or color selecting materials in the focal point ofthe lens system. The imaging system should supply signals appropriatefor determining headlamp dimming control, headlamp on/off control, orboth. The imaging system should also be protected against excessivelight or heat damage.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide images for use in aheadlamp control system.

Another object of the present invention is to provide subwindows in animage array for sensing different color components of the scene.

Still another object of the present invention is to provide an opticalsystem permitting a low resolution image sensor to be used in a headlampcontrol system.

A further object of the present invention is to produce different colorcomponents of a scene using an optical system that does not placefilters in the focal plane of the optical system.

A still further object of the present invention is to sense elevationallight levels for use in determining whether a headlamp should be on oroff in a manner that utilizes an image sensor.

Yet a further object of the present invention is to protect elements ofa headlamp control imaging system from excessive light and heat.

In carrying out the above objects and other objects and features of thepresent invention, an imaging system is provided for use in a vehicleheadlamp control system. The imaging system includes a housing definingan opening, the opening generally towards a scene, an image sensorwithin the housing opposite from the opening, a first lens to focuslight from the scene onto a first portion of the image sensor, and asecond lens to focus light from the scene onto a second portion of theimage sensor, the second portion of the image sensor separate from thefirst portion.

In one embodiment, the first lens focuses light at a first wavelengthonto the image sensor and the second lens focuses light at a secondwavelength onto the image sensor. In a refinement, the focal length ofthe first lens at the first wavelength is substantially the same as thefocal length of the second lens at the second wavelength. In a preferredembodiment, the first lens attenuates light substantially cyan in colorand the second lens attenuates light substantially red in color.

In another embodiment, the image sensor has a low resolution.

In yet another embodiment, a baffle extends from an area between thefirst lens and the second lens towards the image sensor. The bafflereduces light passing through the first lens from striking the secondportion of the image sensor and reduces light passing through the secondlens from striking the first portion of the image sensor.

In a further embodiment, the imaging system includes a shutter forreducing the intensity of light entering the opening. In a preferredembodiment, the shutter is an electrochromic window.

In a still further embodiment, a maximum focal length is the largest ofthe focal length of the first lens and the focal length of the secondlens. The housing defines the opening at least two times the maximumfocal length away from the first lens and the second lens. In yet afurther embodiment, a first portion of the housing defining the openingis positioned to block light which would otherwise travel through thefirst lens and impinge as stray light on the second portion of the imagesensor and a second portion of the housing defining the opening ispositioned to block light which would otherwise travel through thesecond lens and impinge as stray light on the first portion of the imagesensor.

An imaging system is also provided that includes a housing defining anopening generally towards a scene in front of a vehicle, an image sensorlocated within the housing, and a light sampling lens positioned nearthe opening. The light sampling lens gathers light rays from a regiondefined by a vertical arc extending from substantially above the openingto substantially in front of the opening, and redirects the gatheredlight rays towards the image sensor. The lens may gather light rays froma narrow horizontal arc in front of the opening.

In one embodiment, the light sampling lens is further operative togather light rays from elevationally separate regions and to redirectthe gathered light rays from each elevationally separate region to adifferent set of pixel sensors in the image sensor, allowing the imagesensor to detect the light level at different angular elevations. Theelevationally separate regions may be regions separated by 10° ofelevation.

In another embodiment, the system includes a first subwindow of pixelsensors, a second subwindow of pixel sensors, a red lens within thehousing between the light sampling lens and the image sensor forprojecting substantially red components of the redirected light raysonto the first subwindow, and a red complement lens within the housingbetween the light sampling lens and the image sensor, the red complementlens for projecting substantially red complement components of theredirected light rays onto the second subwindow.

A system for controlling at least one headlamp includes a headlampcontroller operative to turn the headlamps on and off based on areceived on/off control signal, an image sensor comprised of an array ofpixel sensors, a lens system operative to gather light rays from aregion defined by a vertical arc extending from substantially above thevehicle to substantially in front of the vehicle and to redirect thegathered light rays towards the image sensor, and a processing andcontrol system operative to read light levels from pixel sensors and todetermine the on/off control signal based on comparing the light levelsto a threshold.

In one embodiment, the processing and control system can determine thethreshold based on color components projected onto the first and secondsubwindows. Alternatively, the processing and control system candetermine whether the region defined by the vertical arc images a bluesky or a cloudy sky and to use a lower threshold for the blue sky thanfor the cloudy sky.

In another embodiment, the processing and control system can determinethe on/off control signal based on comparing the light levels to ahysteretic threshold.

In yet another embodiment, the processing and control system candetermine the on/off control signal based on a time delay from aprevious change in the on/off control signal.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a headlamp control system that may use an imaging systemaccording to the present invention;

FIG. 2 is a schematic diagram of an image sensor according to thepresent invention;

FIG. 3 is an optical system according to the present invention;

FIG. 4 is an enlarged portion of the optical system shown in FIG. 3;

FIG. 5 is an alternative embodiment of an imaging system including abaffle according to the present invention;

FIG. 6 is a schematic diagram illustrating the operation of two lensesfor an embodiment of the present invention;

FIG. 7 is a lens for use in an embodiment of the present invention forheadlamp on/off control; and

FIG. 8 is an illustrative optical system incorporating the lens of FIG.7.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a block diagram of a system incorporating thepresent invention is shown. Headlamp control system 20 is used in avehicle to control one or more of headlamp 22. Control operations mayinclude automatically turning on and off headlamp 22 and automaticallyswitching between high beam and low beam for headlamp 22.

Scene 24 is generally in front of a vehicle. Light rays 26 from scene 24enter imaging system 28 by first passing through optical system 30.Focused rays 32 from optical system 30 strike image sensor 34 in thefocal plane of optical system 30. Processing and control system 36receives image sensor output 38 and produces image sensor control 40.Processing and control system 36 also generate automatic headlampcontrol signal 42 which is received by headlamp controller 44.

Processing and control system 36 may perform continuous cycles to checkfor the presence of headlamps and tail lights in scene 24. During eachcycle, two images are acquired from image sensor 34. As will bedescribed in more detail below, one image has predominantly redcomponents and one image has predominantly red complement components.Bright spots in the red image may indicate the presence of tail lightsin scene 24. Bright spots in both the red and red complement images mayindicate the presence of headlamps in scene 24. Counters may be used toindicate the number of successive frames for which a bright spot hasbeen detected in approximately the same location. Once the count reachesa threshold value, the bright spot is assumed to be from another vehicleand an appropriate action, such as dimming headlamp 22, is taken. Theabove description is a simplification of the embodiments described inU.S. Pat. No. 5,837,994 entitled “CONTROL SYSTEM TO AUTOMATICALLY DIMVEHICLE HEAD LAMPS,” issued Nov. 17, 1998.

Headlamp controller 44 generates headlamp controller signal 46 which isreceived by headlamp 22 causing headlamp 22 to turn on or off or toswitch between a high beam and low beam. Headlamp 22 may produceheadlamp illumination 48, illuminating a portion of scene 24. Headlampcontroller 44 may also receive manual on/off signal 50 from manualon/off control 52 and manual dimmer signal 54 from manual dimmer control56. Manual on/off control 52 and manual dimmer control 56 allow thedriver to manually control the operation of headlamps 22. In analternative embodiment, one or both of headlamp on/off signal 50 andmanual dimmer signal 54 may be used by processing and control system 36to determine the state of headlamp 22.

In an alternative embodiment, shutter 58 is placed before imaging system28. Shutter 58 then receives light rays 26 from scene 24 and outputsattenuated light rays 60 to optical system 30. Shutter 58 reduces oreliminates the amount of light reaching image sensor 34 when light fromscene 24 is excessive such as, for example, at dawn or dusk when the sunis near the horizon. Shutter 58 may be implemented using a mechanicalmeans such as blinds, an iris, or the like, under the control ofprocessing and control system 36 as provided by shutter control signal62. Alternatively, shutter 58 may be a photosensitive glass or plastic.In a further alternative, shutter 58 may be an electrochromic window asdescribed in U.S. Pat. No. 4,902,108 titled “SINGLE-COMPARTMENT,SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC DEVICES, SOLUTIONS FOR USETHEREIN, AND USES THEREOF” to H. J. Byker which is hereby incorporatedby reference.

Image sensor 34 should include a minimum number of sensing elements toreduce processing requirements and decrease cost. To efficiently useimage sensor 34 with a relatively few number of pixel sensors, theprojected image of a distant tail light or headlamp in scene 24 shouldbe comparable in size or smaller than that of a single pixel in imagesensor 34. The relative intensities of color components calculated fromprocessing the image data from such a projected image should begenerally independent of the specific position of the projected image onthe array. Therefore, it is desirable to simultaneously projectdifferently filtered images of scene 24 on spatially separate framespreferably within the same pixel array or alternately in separate pixelarrays. The one or more pixel arrays are preferably on the samesubstrate and in the same package.

A preferred arrangement is to project the separate frames on a commonarray large enough to include the frames in separate subwindows, and touse common control logic which provides a means to simultaneously exposeand process the multiple frames. A control of this type is described inU.S. Pat. No. 5,990,469, entitled “CONTROL CIRCUIT FOR IMAGE ARRAYSENSORS,” issued on Nov. 23, 1999, which is hereby incorporated byreference. Descriptions of the image array and lens systems are providedwith regards to FIGS. 2 through 8 below.

In a preferred embodiment, when a small area light source is detected,the frame is analyzed to determine the single or the small group ofadjoining pixels having illumination levels substantially higher thanthe background level of the surrounding pixels. The light reading isintegrated or summed over this group of pixels with an optionalsubtraction of the average background level. This process is repeatedfor the frame corresponding to each color component. In this manner,readings are relatively independent of whether the illumination iscontained on one pixel sensor or the illumination strikes a pixelboundary and casts portions of light on two or more adjoining pixelsensors. This technique increases the tolerance for a small registrationerror between the subwindows for different color components when theratiometric comparison of the various color components of a given smallarea light source is made.

Referring now to FIG. 2, a schematic diagram representing an imagesensor according to the present invention is shown. Image sensor 34includes an array of pixel sensors, one of which is indicated by 70,arranged in rows and columns. In an exemplary embodiment, image sensor34 includes 80 rows by 64 columns of pixel sensors, most of which arenot shown for clarity. Image sensor 34 includes top border 72, bottomborder 74, left border 76, and right border 78 defining a region coveredby pixel sensors 70. The use of directionality such as, for example,top, bottom, left, and right, is provided for ease of explanation, andis not meant to limit the present invention to a particular orientation.

Image sensor 34 is divided into several subwindows. In one embodiment,two subwindows are used to image scene 24 into two color components.Upper subwindow 94 is bounded by lines 78, 80, 82, and 84, and containspixel sensors 70 struck by an image projected through a lens which isdyed to pass red light. Lower subwindow 96 is bounded by lines 78, 86,82, and 88, and includes pixel sensors 70 onto which an image isprojected through a lens which is dyed to pass cyan or red complementlight.

The lenses provide a field of view of scene 24 such as, for example, 22°wide by 9° high. A space between line 80 and top edge 72 and betweenlines 84 and 90 allow for an elevational adjustment to correct formisalignment of imaging system 28 in the vehicle. To accomplish theadjustment, upper subwindow 94 boundaries, represented by line 80 andline 84 respectively, are moved up or down within the range between topedge 72 and line 90. Similarly, lines 86 and 88 represent boundaries forlower subwindow 96 that may be moved between bottom edge 74 and line 92.In the exemplary embodiment, an elevational adjustment through a rangeof about 4.8° is allowed. Subwindows 94 and 96 are normally moved upwardor downward together but the origin of one relative to the other is alsoadjustable to compensate for variations in the registration of onesubwindow with regards to the other.

Pixel sensors 70 that lie within the region bordered by lines 90 and 92may receive light from both the red and red complement lenses.Therefore, this region is not normally used as part of the activeimaging area. Pixel sensors 70 from this region may be removed to makeroom for other circuits, but because of the relatively small percentageof area lost and the flexibility to use the entire 64×80 pixel array inother applications, leaving pixel sensors 70 in the region bordered bylines 90 and 92 may be of greater benefit. Also, it is not convenient tointerrupt the signal paths along the columns in the array. In theexemplary embodiment, less than 8.5% of pixel sensor 70 fall betweenlines 90 and 92. An embodiment limiting the width required between lines90 and 92 is described with regards to FIG. 5 below. The red and redcomplement lenses are described with regards to FIGS. 3 through 6 andFIG. 8 below.

In an embodiment of the present invention, pixel sensors 70 lyingbetween left edge 76 and line 82 are used for headlamp on/off control.This use is described with regards to FIG. 8 below.

In another embodiment of the present invention, image sensor 34 isdivided into more than two subwindows for imaging scene 24 into aplurality of color components. For example, upper subwindow 94 and lowersubwindow 96 may each be split into two subwindows, creating foursubwindows. The multiple subwindows may be arranged in a two-by-two gridor a one-by-four grid. Spacing between subwindows allows for verticaland horizontal adjustment.

Pixel sensors 70 in image sensor 34 may be charge-coupled devices,photodiodes, or the like. In a preferred embodiment, pixel sensors 70are CMOS active pixel sensors. An APS image sensor is described in U.S.Pat. No. 6,008,486 entitled “WIDE DYNAMIC RANGE OPTICAL SENSOR,” issuedDec. 28, 1999, which is hereby incorporated by reference.

Referring now to FIG. 3, an illustrative embodiment of the presentinvention is shown. Imaging system 28 includes housing 100 with opening102 opening towards scene 24. Image sensor 34 is located within housing100 opposite of opening 102. Support member 104 is located withinhousing 100 and holds red lens 106 and red complement lens 108 betweenimage sensor 34 and opening 102. The support member 104 includes a firstaperture for the first lens and a second aperture for the second lens.Support 104 also prevents light coming through opening 102 from strikingimage sensor 34 unless the light passes through red lens 106 or redcomplement lens 108. The range of pixel sensor 70 used to form topsubwindow 94, namely top edge 72 and line 90, as well as to form bottomsubwindow 96, namely bottom edge 74 and line 92, is indicated on imagesensor 34.

Preferably, opening 102 is located several focal lengths of lenses 106,108 in front of lenses 106, 108. Opening 102 is characterized tominimize the distance between the borders of two images separatelyprojected onto image sensor 34, reducing the amount of optical crosstalkbetween upper subwindow 94 and lower subwindow 96. This is accomplishedby using one border of opening 102 positioned to block light which wouldotherwise travel through lens 108 and impinge as stray light on uppersubwindow 94. Likewise, another border of opening 102 is positioned toblock light which would otherwise travel through lens 106 and impinge asstray light on lower subwindow 96. The use of opening 102 to limitoptical crosstalk is described with regards to FIG. 4 below. A furtherimprovement is to incorporate a baffle positioned between the lenssystems 106, 108 and extending towards image sensor 34 to further reducethe distance required between upper subwindow 94 and lower subwindow 96to adequately minimize optical crosstalk. The use of a baffle isdescribed with regards to FIG. 5 below. As a further extension, a lightcollecting optical system is placed in a portion of opening 102 so thata usable image is projected into a third region of image sensor 34 whilemaintaining adequate optical separation between the three images. Thelight collecting optical system and its application is described inFIGS. 7 and 8 below. Red lens 106 and red complement lens 108 are shownconceptually. An embodiment of the shape and further operation of redlens 106 and red complement lens 108 are described with regards to FIG.6 below.

In an embodiment of the present invention, optical system 30 includesmore than two lens systems 106, 108 to project a plurality of colorfiltered images of scene 24 onto image sensor 34. For example, fourlenses can be arranged in a two-by-two array of lenses. Three of thelenses may pass light in a different color band, such as red, green, andblue, for true color imaging. The fourth lens may pass substantiallyunfiltered light for low light level imaging.

Referring now to FIGS. 3 and 4, the operation of image system 28 willnow be described. Low point 110 represents a distant point in scene 24which is projected as point 112 onto image sensor 34. Low point 110 isat the lower extent of the field of view and projects onto point 112 atthe upper extent of lower subwindow 96 as indicated by line 92 of theunobstructed portion of the image projected by a red complement lens108. Since low point 110 is a distance of typically 50 to 200 metersaway for headlamps of oncoming vehicles and tail lights of rearwardlyapproached vehicles when most headlamp controller actions are initiated,light rays 26 indicated by lower light ray 114, upper light ray 116, andcentral light ray 118 are nearly parallel prior to striking redcomplement lens 108. Red complement lens 108 focuses lower ray 114,upper ray 116, and central ray 118 into point 112 on image sensor 34.Lower aperture edge 120 of opening 102 is positioned so that lower ray114 just clears lower aperture edge 120 and the lower edge of redcomplement lens 108 indicated by 122. With this arrangement, opening 102is just large enough not to block light from low point 110 which wouldotherwise fall on red complement lens 108 to be focused on point 112.

Ray 124 is the most upwardly directed ray which will clear loweraperture edge 120 and pass through red complement lens 108. Compared toray 114, ray 124 traverses a path which is angled upward by anincreasing amount so that it is higher by one lens diameter than ray 114when it enters red complement lens 108 at the top of lens 108 indicatedby 126. This angular deviation of ray 124 from parallel rays 114, 116,and 118 is approximately preserved as ray 124 leaves red complement lens108. Ray 124 strikes image sensor 34 at lower boundary 90 of upper sidewindow 94 at a point indicated by 128.

In one embodiment, red lens 106 and red complement lens 108 have an Fnumber of 4, are nominally 1 millimeter in diameter, and have a focallength, dimension A, of 4 millimeters. Opening 102 is 6 focal lengthsfrom red lens 106 and red complement lens 108. Dimension B for housing100 is about 28 millimeters.

One of the advantages of miniaturization is that opening 102 can bespaced a reasonably large number of focal lengths from red lens 106 andred complement lens 108 without incurring an excessively largestructure. The farther opening 102 is from lenses 106 and 108, the moredistance between lines 90 and 92 can be reduced so that the choice ofspacing from opening 102 to lens 106 and 108 is a practical matter ofbalancing size against lost sensing area.

For the illustrative embodiment described above, ray 124 travelsone-sixth as far from red complement lens 108 to image sensor 34 as fromopening 102 to red complement lens 108. Therefore, ray 124 strikes imagesensor 34 at a point which is approximately one-sixth the diameter ofred complement lens 108 above point 112.

High point 130 is at the upper extent of the field of view of scene 24.The projection of high point 130 through red complement lens 108 strikesimage sensor 34 at a point lower than the region covered by lowersubwindow 96. These rays are not depicted since the projected image isnot within either subwindow 94 or 96.

Since high point 130 is also distant from opening 102, upper ray 132,lower ray 134, and middle ray 136 are substantially parallel prior tostriking red lens 106. Red lens 106 focuses rays 132, 134, and 136 ontopoint 128 on image sensor 134 at the lower boundary of upper subwindow94 as marked by line 90. As with ray 124 described above, ray 138 is themost downwardly directed ray which can pass upper opening edge 140 andstill be focused by red lens 106, striking image sensor 34 at point 112.Thus, while the stray light from red complement lens 108 diminishes tosubstantially zero in going from line 92 to line 90, the stray lightfrom red lens 106 diminishes to substantially zero in going from line 90to line 92.

Referring now to FIG. 5, an alternative embodiment of the presentinvention is shown. FIG. 5 shows the same area of imaging system 28 asseen in FIG. 4. The embodiment depicted in FIG. 5 is the same asdepicted in FIG. 4 with the exception of the addition of baffle 142.Baffle 142 decreases the region of image sensor 34 onto which light fromboth red lens 106 and red complement lens 108 can strike.

As a simplified generalization, for a lens at infinity focus andaperture of diameter d, a stop or baffle which is n focal lengths infront of the lens can be positioned to block rays which would strike thefocal plane at a distance of more than d/n away from the portion of theimage which is unaffected by the stop.

Baffle 142 extends substantially perpendicular to support 104 towardsimage sensor 34. Ideally, baffle 142 would extend until nearly touchingimage sensor 34. However, image sensor 34 may include sensor packagecover glass 144 which may limit the extension of baffle 142.

Baffle 142 blocks ray 124 from striking image sensor 34. With baffle 142in place, ray 146 represents the lowest ray which will clear loweropening edge 120, pass through red complement lens 108, and strike imagesensor 34 at point 148. Point 148 is about two-thirds of the distancefrom line 92 to line 90.

Ray 150 is the most upwardly directed ray which could be focused throughred complement lens 108 and onto image sensor 34 in the absence of loweropening edge 120. Ray 150 strikes image sensor 34 at a point indicatedby 152 well into the area reserved for the image from red lens 106.

There is little room for good optical treatment of baffle 142 and rayssuch as 124 which strike baffle 142 at a shallow angle will reflectsignificantly even from the most blackened surfaces. Opening 102 infront of lenses 106 and 108 performs much better than baffle 142 in theexemplary embodiment shown, but the combination of opening 102 andbaffle 142 gives the best performance in minimizing the distanceseparating upper subwindow 94 and lower subwindow 96 to prevent asignificant amount of light which enters one of lens 106 or 108 fromfalling onto the subwindow projected by the other lens. Note that,instead of spacing subwindows 94 and 96 by the distance between lines 90and 92, this distance could be reduced by applying a baffle similar tobaffle 142 but thinner, by the reduction of subwindow spacing, and byrecentering lenses 106 and 108 and resizing opening 102.

Referring now to FIG. 6, an exemplary embodiment of an aspherical lenspair for use in the present invention is shown. The drawing is providedto illustrate operation of the lenses and not to represent the preciseshape or positioning of the lenses.

Red lens 106 has front surface 200 facing away from image sensor 34 andback surface 202 facing towards image sensor 34. At its farthest point,front surface 204 is located dimension C of 4.25 millimeters from imagesensor 34. Front surface 200 is an ellipsoid described by Equation 1:$Z = {\frac{c\quad r^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {\sum\limits_{n = 2}^{10}{C_{2n}r^{2n}}}}$

where Z is the value of the height of the lens surface along the opticalaxis as a function of the radial distance r from the optical axis, c isthe curvature, k is the conic constant, and the coefficients C_(2n) arethe even order polynomial coefficients. For front surface 200, c equals0.7194 and k equals −0.4529. Rear surface 202 is spherical with a radiusof 4.05 millimeters. The diameter of red complement lens 108, shown asdimension D, is 1.2 millimeters. Red complement lens 108 has athickness, shown as dimension E, of 0.2 millimeters at its center. Thefocal length of red lens 106 is frequency dependent and is 4.25millimeters for a wavelength of 680 nanometers.

Red complement lens 108 has front surface 204 facing away from imagesensor 34 and rear surface 206 facing towards image sensor 34. At itsfarthest point, front surface 200 is located dimension C of 4.25millimeters from image sensor 34. Front surface 204 is also an ellipsoiddescribed by Equation 1 with curvature c equal to 0.7059 and conicconstant k equal to −0.4444. Rear surface 206 is spherical with a radiusof 4.05 millimeters. The diameter of red complement lens 108, shown asdimension F, is 1.2 millimeters. Red complement lens 108 has athickness, shown as dimension E, of 0.2 millimeters at its center. Thefocal length of red complement lens 108 is frequency dependent and is4.25 millimeters for a wavelength of 420 nanometers.

Referring again to FIG. 6, the effects of frequency dependent focallengths in lenses 106 and 108 are described. Due to the differentaspherical front surfaces of red lens 106 and red complement lens 108,red light rays 210 and blue light rays 212 are focused differentlythrough each lens. The focal point for red light rays 210 passingthrough red lens 106 is at the surface of image sensor 34 whereas bluelight rays 212 passing through red lens 106 focus a distance in front ofimage sensor 34. Likewise, blue light rays 212 passing through redcomplement lens 108 focus onto the surface of image sensor 34 and redlight rays 210 passing through red complement lens 108 focus a distancebehind the surface of image sensor 34.

In a preferred embodiment, red lens 106 is manufactured from a polymerwhich includes a dye for reducing the magnitude of red complement lighttransmitted through red lens 106. Red complement lens 108 ismanufactured from a polymer which includes a dye for reducing themagnitude of red light transmitted through red complement lens 108. Asan alternative, at least one surface of red lens 106 and red complementlens 108 may be coated to achieve red filtering and red complementfiltering respectively. A further alternative is to use separate filtersbetween scene 24 and image sensor 34. In particular, filters may beattached to support 104 either directly in front of or in back of lenses106 and 108.

In an embodiment of the present invention, more than two lenses 106, 108are used. Each lens may be dyed or tinted to admit a different colorfrequency. Preferably, each lens is shaped such that the focal length ofany lens 106, 108 at the pass frequency of that lens is the same as thefocal length of any other lens 106, 108 at the pass frequency of theother lens.

Referring now to FIG. 7, a lens for use in an embodiment of the presentinvention for headlamp on/off control is shown. Light sampling lens 250collects light from a range of directions, shown as rays 251 through260, from the horizontally forward direction to the vertically upwarddirection. The inclinations of rays 251 through 260 are spaced inapproximately 10° increments. Lens 250 redirects incoming rays 251through 260 to outgoing rays 261 through 270 along approximatelyhorizontal paths.

Approximately vertical ray 251 is refracted to ray 271 at front surface272 of lens 250. Ray 271 is internally reflected to ray 273 at surface274 and ray 273 is refracted to ray 261. Surface 275 is approximatelyparallel to ray 271 or is at an angle with surface 274 slightly largerthan the angle which would place surface 275 parallel to ray 271. Ifsurface 275 is at an angle with surface 274 less than the angle whichwould place surface 275 parallel to ray 271, ray 271 would be blockedwhen ray 251 entered at a higher point on surface 272, thereby castingan objectionable shadow on surface 274 close to the intersection of ray271 with surface 275. Lens 250 bends incoming rays 252 through 255 in asimilar manner to produce outgoing rays 262 through 265. Surface 274forms the lower side and surface 275 forms the upper side of atriangular feature with a vertex pointing generally away from frontsurface 272.

Ray 256 is refracted at surface 280 to ray 281 and ray 281 is refractedto ray 266 at back surface 282. Similarly, ray 257 is refracted bysurface 283 to become ray 284, which is refracted by back surface 282 tobecome ray 267. Surface 285 is approximately parallel to ray 281 andsurface 286 is oriented to approximately bisect the angle between ray256 and ray 284. Lens 250 refracts incoming rays 258 through 260 in asimilar manner to produce outgoing rays 268 to 270. Surface 280 formsthe lower side and surface 285 forms the upper side of a triangularfeature with a vertex pointing generally away from back surface 282.

In a preferred embodiment of lens 250, outgoing rays 261 through 270 areangled progressively from slightly downward for ray 261 to slightlyupward for ray 270.

In one embodiment, lens 250 is formed from acrylic with a cross sectionas shown in FIG. 7 throughout. This embodiment will collect light in avertically oriented 90° fan with a relatively small angle in thehorizontal direction. In an alternative embodiment, increased horizontalcoverage is obtained by modifying front surface 272 and back surface282. Surface 272 can be formed with a concave cylindrical shape, withthe axis of the cylinder parallel to the length of lens 250. Surface 282can be formed with a negative cylindrical shape, the axis of thecylinder again parallel to the length of lens 250.

Referring now to FIG. 8, an illustrative optical system incorporatingthe lens of FIG. 7 is shown. Baffle 300 is placed between scene 24 andlenses 106 and 108. In a preferred embodiment, baffle 300 is part ofhousing 100. Baffle 300 is angled at an angle θ of approximately 45°with vehicle horizontal. Baffle 300 defines opening 302 opening towardsscene 24 in front of the vehicle. Opening 302 may be trapezoidal suchthat the projection of aperture 302 onto a vertical surface would form arectangle on the vertical surface similar to aperture 102. Aperture 302is as small as possible without restricting light projected by lens 106to any point in upper subwindow 94 or by lens 108 to any point in lowersubwindow 96.

Lens 250 is mounted in one side of opening 302. The width of lens 250 isapproximately the same as the diameter of lens 106 or 108. Lens 250 isoriented such that ray 251 comes from approximately above the vehicleand ray 260 comes from approximately in front of the vehicle. Lens 250is positioned so that a blurred, inverted image of lens 250 is projectedby red lens 106 onto one edge of image sensor 34 between line 304 andline 306 to form red sky image 312. Lens 250 is also positioned so thata blurred, inverted image of lens 250 is projected by red complementlens 108 onto one edge of image sensor 34 between line 308 and line 310to form red complement sky image 314. Due to parallax error, line 306 isabove the lower edge of upper subwindow 94 and line 308 is below lowersubwindow 96. The active length of lens 250 is made short enough topermit the entire active length to be projected on the regions betweenlines 304 and 306 and between lines 308 and 310.

Red sky image 312 and red complement sky image 314 are scanned intoprocessing and control system 36. Since only a coarse image is requiredfor headlamp on/off control, it is not a great detriment that red skyimage 312 and red complement sky image 314 are not in focus. In oneembodiment, a threshold is compared to the light levels detected byimage sensor 34. If the light levels are above the threshold, headlamp22 is turned off. If the light levels are below the threshold, headlamp22 is turned on.

The pixel locations for red sky image 312 and red complement sky image314 are correlated so that readings can be compared for each 10°elevational increment. A higher ratio of red complement indicates thatblue sky is being viewed. In one embodiment, a lower threshold point maybe used to turn headlamp 22 on or off for a blue sky than for a cloudysky.

In another embodiment, the threshold is hysteretic. In still another, atime delay after the last on/off transition is used. These twoembodiments may prevent headlamp 22 from frequent on-off transitionsaround the switch point.

While the best modes for carrying out the invention have been describedin detail, other possibilities exist within the spirit and scope of thepresent invention. Those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

The invention claimed is:
 1. A system for controlling at least oneheadlamp comprising: a headlamp controller in communication with theheadlamps, the headlamp controller operative to turn the headlamps onand off based on a status of a received on/off control signal; an imagesensor comprised of an array of pixel sensors; a lens system operativeto gather light rays from a region defined by a vertical arc extendingfrom substantially above the vehicle to substantially in front of thevehicle and to redirect the gathered light rays towards the imagesensor; and a processing and control system in communication with theimage sensor and the headlamp controller, the processing and controlsystem operative to read light levels from pixel sensors and todetermine the status of the control signal based on comparing the lightlevels to a threshold.
 2. A system for controlling at least one headlampas in claim 1, wherein said lens system includes a light sampling lensand the system further comprises: a first subwindow of pixel sensors; asecond subwindow of pixel sensors; a red lens within the housing betweenthe light sampling lens and the image sensor, the red lens operative toproject substantially red components of the redirected light rays ontothe first subwindow; and a red complement lens within the housingbetween the light sampling lens and the image sensor, the red complementlens operative to project substantially red complement components of theredirected light rays onto the second subwindow.
 3. A system forcontrolling at least one headlamp as in claim 2 wherein the processingand control system is further operative to determine the threshold basedon color components projected onto the first and second subwindows.
 4. Asystem for controlling at least one headlamp as in claim 2 wherein theprocessing and control system is further operative to determine whetherthe region defined by the vertical arc images a blue sky or a cloudy skyand to use a lower threshold for the blue sky than for the cloudy sky.5. A system for controlling at least one headlamp as in claim 1 whereinthe processing and control system is further operative to determine thestatus of the on/off control signal based on comparing the light levelsto a hysteretic threshold.
 6. A system for controlling at least oneheadlamp as in claim 1 wherein the processing and control system isfurther operative to determine the status of the on/off control signalbased on a time delay from a previous change in the status of the on/offcontrol signal.
 7. A system for controlling at least one headlampcomprising: an imaging system operative to gather light from a scene infront of the at least one headlamp and to determine the intensity of thegathered light; a shutter between the imaging system and the scene, theshutter operative to attenuate the intensity of light from the scene;and a processing and control system in communication with the imagingsystem and the shutter, the processing and control system operative toread light levels from the imaging system and to control the shutterattenuation of light based on the light levels.
 8. A system forcontrolling at least one headlamp as in claim 7 wherein the shutter isan electrochromic window.
 9. A system for controlling headlamps of avehicle, said system comprising: vehicle headlamps; at least one firstlight sensor operable to output a first signal responsive to lightincident on a surface of the at least one first light sensor; at leastone second light sensor operable to output a second signal responsive tolight incident on a surface of the at least one second light sensor; alens system operable to collect light from above a vehicle and directthe collected light onto the at least one first light sensor and tocollect light from in front of the vehicle and direct the collectedlight onto the second light sensor, whereby the first signal isproportional to the light level above the vehicle and the second signalis proportional to the light level in front of the vehicle; and aprocessing and control system coupled to the vehicle headlamps, the atleast one first light sensor, and the at least one second light sensor,the processing and control system operable to control the headlampsresponsive to at least the first and second signals.
 10. The system ofclaim 9, wherein the lens system includes a first lens for directinglight from above the vehicle to the at least one first light sensor. 11.The system of claim 10, wherein the first lens also directs light fromin front of the vehicle.
 12. The system of claim 11, wherein the lenssystem further includes a second lens for focusing light directed fromabove the vehicle by the first lens onto the at least one first lightsensor.
 13. The system of claim 12, wherein the lens system furtherincludes a third lens for focusing light from in front of the vehicleonto the at least one second light sensor.
 14. The system of claim 10,wherein the lens system further includes a second lens for focusinglight directed from above the vehicle by the first lens onto the atleast one first light sensor.
 15. The system of claim 14, wherein thelens system further includes a third lens for focusing light directedfrom in front of the vehicle by the first lens onto the at least onesecond light sensor.
 16. The system of claim 10, wherein the lens systemfurther includes a second lens for focusing light from in front of thevehicle onto the at least one second light sensor.
 17. The system ofclaim 9, wherein the lens system includes a first lens for directinglight from in front of the vehicle to the at least one second lightsensor.
 18. The system of claim 17, wherein the lens system furtherincludes a second lens for focusing light directed from in front of thevehicle by the first lens onto the at least one second light sensor. 19.The system of claim 9, wherein the at least one first light sensorcomprises at least one pixel of an image array sensor.
 20. The system ofclaim 9, wherein the at least one second light sensor comprises at leastone pixel of an image array sensor.